Léonard Lessius was a Flemish Jesuit whose published works engaged in the most pressing economic, theological, and philosophical debates of the late sixteenth and early seventeenth-centuries. Highly-respected for both his profound intellect and his exemplary integrity and virtue, Lessius, also known as "The Prince of Philosophers" was venerated even in death. Despite his remarkable fame and influence in his own day, Lessius' philosophical contributions and legacy have been largely forgotten by modern historians. This striking lacuna in the historiography illuminates the narrow categories and concerns as well as the serious limitations of modern philosophy and the history of philosophy in particular. This report narrows in on one of these lost philosophical fields and treatises in particular, Lessius's study on diet and health, Hygiasticon (Antwerp, 1613). It uniquely, and quite literally, gets at the heart and soul of early modern philosophy: what is natural, what is the relationship between body, mind and soul, and what is necessary for health, wealth, spiritual- and self-improvement. / text